Thread-cutting mechanism for sewing machines



March 10, 1925. r 1,529,020

' ;A. F. FIFIELD THREAD CUTTING MECHANISM FOR SEWING MACHINES Filed Aug.14, 1922 3 Sheets-Sheet 1 k WITNESSES:

ATTORNEY March 10, 1925. 1,529,020,

A. F. FIFIELD THREAD CUTTING MECHANISM FOR SEWING MACHINES File Aug. 14,1922 5 Sheets-Sheet 2 WITNESSES: Q INVENTOR z $2.22, mam

March 10; 1925.

A. F. F' IFIE LD THREAD CUTTING MECHANISM FOR SEWING MACHINES 3 Sheets-5 |NVENTOR Q WITNESSES! ww Z g 1%,

Patented Mar. 10, 1925.

UNITED STATES PATENT OFFICE.

ALBERT F. 'FIFIELD, OI! NEWARK, NEW JERSEY, ASSIGNOR TO THE SINGER MANU-FACTURING COMPANY, OIE ELIZABETH, NEW JERSEY, A CORPORATION OF NEWJERSEY.

, THREAD-CUTTING MECHANISIM FOR SEWIN G'WIACHINES.

.To all whom it may concern}:

Be it known that I, ALBERT F. FIFIELD, a citizen of the United States,residing at Newark, in the county of Essex and State of New Jersey, haveinvented certain new and useful Improvements in Thread-CuttingMechanisms for Sewing Machines, of

which the following is a specificati0n,.reference being had thereintothe accompanying drawings.

v This invention relates to thread-cutting mechanism for sewing machinesand has for a particular object to improve the mechanism disclosed in myPatent N 0. 1,447,941 of March 6, 1923. In the device of my saidcopending application it is found that at high speeds there is somedanger of the supply limb of the needle-loop being sheared ofi',together with the work-limb, whereby the thread-end hanging from theneedle will be of insufficient length to enable the next sewingoperation to be properly started.

Furthenin the device of my said application, the bobbin-thread nippercomprises a spring which presses directly against the needle-loopdetaining blade and both the bobbin-thread and the supply limb of theneedle loop are caught by the .nipper just before the threads are out.Thus, when the work is removed and the needle-thread end hanging fromthe needle is thereby pulled out of the-nipper, said needle-thread endwill sometimes drag the bobbin-thread end out of the nipper andconsequently prevent the bobbin-thread end from beingiheld under controlwhen the initial stitch of the' n'ext sewing operation is formed.

Further, with my prior device, difficulty is occasionally experienced inproviding a beginning needle-thread end uniformly long enough to begripped by the thread-wiper 'below the throat-plate at the beginning ofasewing operatiombut not so long as tosti'ck out from the finished work.

The present improvement seeks to refine my prior construction andeliminate the sources of the minor difficulties above enumerated totheiend that still greater certainty and uniformity of operation will:be secured and a uniformly satisfactory prod-- not more easilyattained.

It is more generally an object of the Application filed. August 14,1922. Serial no. 581,606.

present invention to provide a sewing machine having thread-severingmechanism of greater simplicity, durability and dependability than hasheretofore been attained.

To the accomplishment of the ends in view, the shank of the ledger-bladeof my prior construction has been reversed in posi- [1011 so as to liewithin the circular path of action of the needle-loop detaining and:severing blade.

passes freely between the nipper-blades and the needle loop detainingblade.

To insure a beginning thread-end of a minimum uniform length, aledger-blade has been added .to cooperate with a sharpened edge on thethread-wiper to cut off anyexcess needle-thread projecting beyond thewiper. This ledger-blade is formed with astraight, easily sharpened edgeand. to insure certainty of action, an additional blade having athread-guiding edge in clined to the cutting edge of the ledger-blade isassociated with the latter to afford, in effect, a V-notch insuringagainst escape of the needle-thread end from cutting position betweenthe sharpened edge of the thread wiper and its cooperative ledger-blade.

In the accompanying drawings, Fig. 1 is a rear side elevation of asewing machine embodying the invention. Fig. 2 is a bot tom plan view ofthe machine. Fig. 3 is a cross-section through the sewing pointlongitudinallygof the machine bed. Fig. 4

.is a bottom plan view of the throat -plate showing the thread=cuttingfand nipping i111- plements carried thereby. n Fig. 5 is view of thethread-cutting and nipping implement looking in the direction ofthe'iarrow 55, Fig. at. Fig. 6 is'a bottom plan view of the needleeloopdetaining and severing "the needle-loop detaining and severing blade tosever the needle and bobbin-threads.

In the preferred embodiment of the invention. as illustrated, 1represents the machine bed from which rises the standard 2 of theoverhanging bracket-arm 3 terminating in the head i in which isjournaled to reciprocate the needle-bar 5 carrying the eye-pointedneedle 6.

The needle 6 cooperates with a loop-taker 7 which is preferably in thetorm of a rotary hook operating to give the needle-loop half twist incasting it about the usual bobbin in the thread-case 8, thereby juxtaposing the bobbin-thread and the work-limb of the needle-loop, as explainedin my said copending application. and enabling the needle and bobbinthreads to be cut together at a point close to the work by means of aneedle loop detaining and severingblade having but one cutting edge. Theroi'ary hook 7 is mounted on the shat't 9 which at its rearward end isgeared at 10 to the shaft 11 extending vertically within the standard 2and at its upper end geared at 12 to the main-shaft 13.

The main-shaft 13 is connected as usual to drive the ueedle bar 5 andthe, teed-cam '14 which latter operates through the usual connections tomove the work-clamp 15 back and forth over the bed 1 and thus determinethe placing of the stitches. the present machine is intended for sewingon buttons. the work-clamp 15 is of the usual button holding typedisclosed. for example. in the patent to C. M. Horton. No. 667,676. ofDecember 19, 1905.

The present machine is equipped with a stop-motion device. constructedsubstantially in accordance with the disclosure of my said patent andincluding the stop-motion lever 16 which carries the belt-shifter 17adjacent the tight and loose pulleys 18. 19. respectively. on themain-shaft 13. The lever 16. as shown in full lines in Fig". 1. isinstopping position. It may be tilted about its pivot 17 to dotted lineposition to start the machine. Atthe end of the sewing operation thelever 16 is automatically released and springs to full line or stoppingposition. whereupon a vertically spring pressed plunger 20 carried bysaid lever engages a notch in a stopping cam 21 on the mainshatt 13. Thelever 16 is so mounted that it may partake of a sidewise. overthrowmovement under the action of the stopping cam 21 in coming to rest. Thisoverthrow movement is balanced by the usual butler spring (not shown)and brings the mainshaft 13 to rest without destructive shock. Thepresent stop-motion device preferably has incorporated therewith abraking device permitting" high speed operation. as disclosed in my saidpatent. The present improvement. however. is not concerned with themechanism of the braking device and a description of the latter istherefore deemed unnecessary. In so far as the present improvement isconcerned the stop-motion lever 16 is constructed and operatedsubstantially in accordance with the disclosure of said Horton patent.

Mounted below the bed 1 is the usual thread-cutter operating slide-bar22 which in the present instance is connected at its rear end by meansof a link 23 to a lever 2 pivoted at 25 to the bed 1. The lever 25 isconnected by a link 26 to an auxiliary slidebar 2'? which at the end ofthe sewing operation is given the usual two-stage movement; the firststage of such movement being given by the cam-operated lever 28 and thesecond stage by the overthrow of the stopmotion lever which istransmitted to the slide-bar 27 through the usual bellcranklever 29.This mechanism for imparting: to a threadu'utter operating slide-bar atwo stage univement is old in the art and is disclosed in said Hortonpatent.

The in'ipleinents ot the. present threadcutting; mechanism are mountedon the usual throat-plate 30 from the under side of which projects thepivot-post 31 for the threadcutter lever-arm 32. The lever-arm 32 isconnected to the slidebar 22 by means of the link 353. The lever-arm 32has mounted thereon a needle-loop detaining blade S t. similar in shapeand function to that dis closed in in said patent. Such blade has at itsouter edge an upstanding lip trans verse to the plane oi the blade 34and having its inner forward edge 36 sharpened as shown in Figs. -'land6. The projection 33 is opcrutively received in the circular clearancegroove 3T in the throat-plate.

The cutting edge 36 of the blade 3 i co operates with the ledger-blade36 which. together with its shank 39, is disposed within the circle ofoperation 0. Fig. 6. (ii the cutting lip 35. By sharpening the innertorward edge 36 of the lip 35. instead ot the outer edge. and bydisposinc the ledgerblade 38 within, rather than outside ot. thecircular path oi. movement of the cutting lip it will be seen uponreferring to Fig.

I 3 that the cutting edge 36 is set inwardli.

from the outer edge 40 of the loop-detaining blade 34. therebyovercoming the possibility of the supply or lower limb s of theneedlcloop getting" in the path of the cutting blade.

The needle-loop detainingblade 34: has its shank 41 (Fig. 7) oftsetbelow the plane ot the blade 34 proper. The shank 41 is secured to thecarrier arm 32 by means of the screw 12 which also serves to secure apair of bobbin-thread nipper-blades 43. it in a position spaced belowthe needle-loop detaining blade 34. The blade 43 is preferably maderelatively stilt and the blade 44-. springy. The ends of these bladesare oppositely curved to form a mouth 45. Fig. 1, which catches thebobbin-thread b. and

of the carnier l'evel" 32.

' When themachine is' sewing, the carrier-- lever 32 and blades 34, 43and 44 occupy a retracted position indicated in dotted lines;

in Fig. 4. As the sewing-operationis nearing completion the usualthread-cutter operatmg;camsgroove 46 in the teed-wheel 14" actingthrough the lever 28, imparts to the slide-rod 22 its first stage. ofmovement which causes the needle-loop detaining blade 34 to be projectedinto the last needleloop as the latter is being passed around the bobbinby the rotary hook 7. After the take-up has acted, the last needle-loopis thus detained below the work in a spread condition by the blade 34.The inner edge of the blade 34 also catches the bobbinthread I) anddirects said thread into the mouth of the nipper 43, 44, at the sametime serving to pull off enough bobbinthread to insure the interlockingof the latter with the needle-thread when the initial stitch of the nextsewing operation is formed. The supply limb of the needle-loop passesfreely between the loop-detaining blade 34 and the upper-blades 43, 44,while the work-limb 'w of the needle-loop and the bobbin-thread b extendin juxtaposed relation above the blade 34 directly in the path of thecutting lip 35, and between the latter and the ledger-blade 38, as shownin Fig. 3. Theoverthrow motion of the stop-lever 16, in bringing themain-shaft 15 to rest, operates in the usual manner to impart the secondstage of movement to the slide-bar 22 which transmits to the blade 34 acutting impulse carrying the lip 35 into shearing engagement with theledger-blade 38 and thereby severing the bobbin-thread Z) and thework-limb 'w of the needle-loop close to the work.

Mounted on the carrier-lever 32 is a thread-wiper or gripper 47 of usualhooked form which is adapted to nip the beginning end of theneedle-thread against the under side of the throat-plate 30. In thepresent instance the edge 48 of the thread-gripper is sharpened forcooperation with the sharpened straight edge 49 of a ledger-blade 50secured to the throat-plate 30, to cut off any excess of needle-threadsticking out beyond the gripper and thus insure a needle-thread end of auniform minimum length, i. e., no longer than is essential to the secureholding of such thread-end by the gripper 47 during the formation of theinitial stitches. A second blade 51 having a thread-guiding point 52underlying the cutting edge 49 and directed at an angle to the latter isprovided "for catching the needle-thread end and directing it to thecutting edge 49 of the ledgerblade 50. The finger 52 together with thecutting edge 49 forms a. V-notch insuring against escape 3of=the thread.This construct'ion:has an advantage over a single ledgerblarle formedwith a V-notchin =that the straight cutting edge 49 may be separatedtromnthe finger' 52' and easily sharpened on a-n ordinary grindingwheel.

l'la-ving thus-set fortluthe nature otthe invention; what I claim:herein is:

1. I n ausewing'maclri ne, the combination with a throat-plate, of aneedle-loop detaining blade mounted below the throat-plate to swingabout an axis transverse to the plane of the throat-plate, said bladehaving a blunt outer curved edge and a portion extending toward saidthroat-plate, said portion having a cutting edge disposed inwardly fromsaid outer edge.

2. In a sewing machine, the combination with a throat-plate, of aneedle-loop detaining blade mounted below the throat-plate to swingabout an axis transverse to the plane of the throat-plate, said bladehaving a blunt outer curved edge and a cutting edge disposed inwardlyfrom said outer edge, and a ledger-blade mounted inwardly from saidcutting edge and cooperating with the latter to sever the thread. i

3. In a sewing machine, the combination with a throatplate, of aneedle-loop detaining blade mounted below said throat-plate on an axistransverse to the plane of the throat plate, and a bobbin-thread nippermounted in spaced relation with and below said needle-loop detainingblade.

4. In a sewing machine, the combination with throat-plate, of a carriermounted on the under side of said throat-plate, a needle-loop detainingblade mounted on said carrier, and a bobbin-thread nipping device alsomounted on said carrier in spaced relation with said needle-loopdetaining blade so as not to nip the thread of the needle-loop.

5. A thread-cutting mechanism for sewing machines comprising, aflattened needleloop detaining blade pivoted transversely of the planesof its faces and having a curved outer edge and a cutting lip disposedat said outer edge and at an angle to the faces of said blade, said liphaving a cutting edge disposed inwardly from the outer edge of saidblade.

6. In a sewing machine, the combination with a threadwiper in the formof a hook adapted to grip the beginning end of the needle-thread belowthe work and having adjacent its hooked extremity a rearwardly directedcutting edge, of a ledger-blade having a straight sharpened edge, and asecond blade detachable from said ledger-blade and formed with athread-guiding edge disposed at an angle to said ledger-blade andforming therewith a V-notch, substantially as and for the purposesspecified.

7. The combination With stitch-forming mechanism including areciprocating needle, a bobbin and a rotary hook adapted to give theneedle-loop a half twist in casting it about the bobbin and juxtaposethe bobbinthread and the Work-limb of the needle-loop, of a needle-loopdetaining and severing blade having a bobbin-thread pull-off edge, apair of bobbin-thread nipper-blades spaced from said blade and adaptedto seize only the bobbin-thread While permitting the 10 needle-loop topass freely between the needleloop detaining blade and thenipper-blades, and means for severing the juxtaposed threads.

In testimony whereof, I have signed my 15 name to this specification.

ADBERT F. FIFIELD.

